Rankine cycle system

ABSTRACT

A Rankine cycle system includes: a superheater, an expander including a first outlet discharging steam and a second outlet discharging liquid refrigerant produced therein; a first discharge path discharging the steam from the expander; a condenser condensing the steam introduced through the first discharge path into liquid refrigerant, a condensed water tank reserving the liquid refrigerant produced in the condenser; and a second discharge path discharging the liquid refrigerant from the expander to the condensed water tank, wherein a liquid level in the condensed water tank satisfies a following relation: Δh&gt;ΔPto/ρg, when Δh means a height difference between the liquid level and a lowest liquid level in the second discharge path, ΔPto means a pressure loss when the steam flows into the condenser from the expander through the first discharge path, ρ means a density of the liquid refrigerant, and g means a gravitational acceleration.

TECHNICAL FIELD

The present invention relates to a Rankine cycle system.

BACKGROUND ART

There has been conventionally known a Rankine cycle that recovers exhaust heat generated due to operation of an internal-combustion engine. An exemplary Rankine cycle makes a water-cooled cooling system of an engine have a sealed structure to carry out the ebullient cooling, drives an expander such as a steam turbine by refrigerant vaporized by exhaust heat of the engine, i.e. steam, and recovers exhaust heat by converting thermal energy included in the steam into electrical energy, for example. Patent Document 1 is one example that improves the above-described Rankine cycle system.

PRIOR ART DOCUMENT Patent Document

-   [Patent Document 1] Japanese Patent Application Publication No.     2009-103060

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

However, a following inconvenience may occur at a time of cold start of an internal-combustion engine by adopting an approach of Patent Document 1, for example. A temperature of an expander is generally low when the internal-combustion engine is cold. If steam is supplied to the expander in a low temperature state, the steam is condensed in the expander, and goes back to liquid refrigerant. The liquid refrigerant produced in the expander is retained in the expander, becomes a resistance against the drive of the expander, and may cause deterioration or damage of the expander. When a Rankine cycle system is implemented to a vehicle, it is necessary to solve the problem of deterioration or damage of the expander described above because the expander frequently becomes in a cold state. It is considered to provide a control valve that controls inflow of steam into the expander while the internal-combustion engine is warmed up, in order to suppress the deterioration and damage of the expander. However, the above-described control needs an actuator that actuates the control valve, and a temperature sensor to set a control timing or a development of a logic to estimate the temperature, and thus increases cost.

Therefore, a problem to be solved by a Rankine cycle system disclosed in the present specification is to suppress deterioration and damage of an expander caused by production of liquid refrigerant in the expander such as a steam turbine.

Means for Solving the Problems

To solve the above-described problem, a Rankine cycle system disclosed in the present specification is characterized by including: a superheater, an expander that is driven by steam, which is vaporized refrigerant supplied from the superheater, to recover energy, and includes a first outlet discharging steam and a second outlet discharging liquid refrigerant produced by condensation of the steam in the expander; a first discharge path that is connected to the first outlet and discharges the steam from the expander; a condenser into which the steam is introduced through the first discharge path, and that condenses the steam into liquid refrigerant, a condensed water tank that reserves the liquid refrigerant produced in the condenser; and a second discharge path that connects the second outlet to the condensed water tank and discharges the liquid refrigerant from the expander.

The expander has the second outlet, and thus is able to discharge the liquid refrigerant produced by condensation in the expander when the expander is in a cold state. If the liquid refrigerant can be discharged from the expander, it is possible to reduce drive load of the expander. As a result, the deterioration and damage of the expander can be suppressed.

It is desirable that the second outlet is provided to a downside portion of the expander. It is for discharging the liquid refrigerant efficiently regardless of an inner shape of the expander and the like. Generally, the liquid refrigerant can be discharged by providing the second outlet to the downside portion of the expander.

It is desirable that a liquid level in the condensed water tank satisfies a following relation: Δh>ΔPto/ρg, when a difference between the liquid level and a lowest liquid level in the second discharge path is expressed by Δh, a pressure loss when the steam flows into the condenser from the expander through the first discharge path is expressed by ΔPto, a density of the liquid refrigerant is expressed by ρ, and a gravitational acceleration is expressed by g.

If the liquid level in the condensed water tank is maintained so as to satisfy the above-described relation, it is possible to prevent the steam from flowing through the second outlet.

A connected position of the second discharge path to the condensed water tank may be located higher than the lowest liquid level in the second discharge path. For example, when the second discharge path is formed of a U-tube, the second discharge path is a U-shaped portion of the U-tube, and Δh can be set large. If Δh is set large, it is possible to prevent the steam from flowing through the second outlet effectively.

Furthermore, a diameter of the second outlet may be smaller than a diameter of the first outlet. It is possible to prevent the steam from flowing through the second outlet effectively by setting a relation between the diameter of the first outlet and the diameter of the second outlet so as to satisfy the above-described relation. In addition, if the diameter of the first outlet becomes large, the pressure loss ΔPto can be reduced, and this is effective for preventing the steam from flowing through the second outlet.

In addition, it is desirable that a flow passage area of the second discharge path is smaller than a flow passage area of the first discharge path. For example, the relation expressed by the above equation can be achieved by making an inside diameter of a pipe forming the second discharge path smaller than an inside diameter of a pipe forming the first discharge path. It is possible to prevent the steam from flowing through the second outlet by making a relation between the flow passage area of the second discharge path and the flow passage area of the first discharge path satisfy the above-described relation. In addition, if the flow passage area of the first discharge path becomes large, the pressure loss ΔPto can be reduced, and this is effective for preventing the steam from flowing through the second outlet.

Effects of the Invention

According to the Rankine cycle system disclosed in the present specification, it is possible to suppress deterioration and damage of an expander caused by production of liquid refrigerant in the expander.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic configuration diagram of a Rankine cycle system of an embodiment;

FIG. 2 is an explanatory diagram enlarging a part A in FIG. 1; and

FIG. 3 is an explanatory diagram illustrating another shape of a second discharge path.

MODES FOR CARRYING OUT THE INVENTION

Hereinafter, a description will be given of modes for carrying out the present invention in detail with reference to drawings.

Embodiment

A description will be given of an outline structure of a Rankine cycle system 100 with reference to FIG. 1 and FIG. 2. FIG. 1 is a schematic configuration diagram of the Rankine cycle system 100. FIG. 2 is an explanatory diagram enlarging a part A in FIG. 1. The Rankine cycle system 100 has an engine 1 that is cooled by boiling of refrigerant therein. The engine 1 is an example of an internal-combustion engine corresponding to a steam generator. The engine 1 includes a cylinder block 1 a and a cylinder head 1 b. A water jacket is formed in the cylinder block 1 a and the cylinder head 1 b, and the engine is cooled by boiling of the refrigerant in the water jacket. The engine 1 produces steam at this time. The engine 1 further includes an exhaust pipe 2. One end of a steam pathway 3 is connected to the cylinder head 1 b of the engine 1.

A gas-liquid separator 4 is arranged in the steam pathway 3. The gas-liquid separator 4 separates the refrigerant, which is in a gas-liquid coexistence state and flows into the gas-liquid separator 4 from the engine 1 side, into a gas phase (steam) and a liquid phase (liquid refrigerant). One end of a refrigerant circulating path 5 is connected to a bottom end portion of the gas-liquid separator 4. The other end of the refrigerant circulating path 5 is connected to the cylinder block 1 a. In addition, in the refrigerant circulating path 5, arranged is a first water pump 6 that pumps the liquid refrigerant into the engine 1. The first water pump 6 is a so-called mechanical pump, and uses a crankshaft included in the engine 1 as a drive source. The first water pump 6 circulates the liquid refrigerant between the engine 1 and the gas-liquid separator 4.

A superheater 8 is arranged in the steam pathway 3. The superheater 8 includes a vaporizing portion 8 a at a lower side, and a superheating portion 8 b at an upper side. The exhaust pipe 2 is led to the superheater 8. Exhaust gas generated in the engine 1 flows through the exhaust pipe 2. The exhaust pipe 2 passes through the superheater 8 so that the exhaust gas passes through the superheating portion 8 b and the vaporizing portion 8 a in this order. One end of a liquid refrigerant pathway 7 is connected to the vaporizing portion 8 a. The exhaust gas exchanges heat with the steam passing through the gas-liquid separator 4. The other end of the liquid refrigerant pathway 7 is connected to the bottom end portion of the gas-liquid separator 4. An opening/closing valve 7 a is provided to the liquid refrigerant pathway 7. An opened/closed state of the opening/closing valve 7 a determines the supply of the liquid refrigerant from the gas-liquid separator 4 to the vaporizing portion 8 a. The liquid refrigerant supplied to the vaporizing portion 8 a is vaporized by heat of the exhaust gas that has superheated the steam at the superheating portion 8 b. This increases a steam generation amount, improves the degree of superheating of the steam, and improves recovery efficiency of the exhaust heat. A steam discharge pipe 3 a is provided to an upper end portion of the superheating portion 8 b. A nozzle 9 is provided to a tip end portion of the steam discharge pipe 3 a.

An expander 10 is arranged at a downstream side of the superheater 8. The expander 10 is driven by vaporized refrigerant, i.e. steam, supplied from the superheater 8, and recovers energy. The expander 10 is a steam turbine including a chassis 10 a and a turbine blade 10 b located in the chassis 10 a. The nozzle 9 is mounted to the chassis 10 a so that the steam supplied through the steam pathway 3 is injected toward the turbine blade 10 b. Thus, the turbine blade 10 b is rotary driven by the steam supplied through the steam pathway 3. The rotative force of the turbine blade 10 b assists the rotation of the crankshaft included in the engine 1, and drives a power generator. This recovers the exhaust heat.

The chassis 10 a of the expander 10 is provided with a first outlet 10 a 1 that discharges the steam, and a second outlet 10 a 2 that discharges the liquid refrigerant produced by condensation of the steam in the chassis 10 a. Here, the second outlet 10 a 2 is provided to a downside portion of the chassis 10 a of the expander 10 so as to discharge the liquid refrigerant in the chassis 10 a of the expander 10. A diameter D2 of the second outlet 10 a 2 is smaller than a diameter D1 of the first outlet 10 a 1. That is to say, a relation of D2<D1 is established.

One end of a first discharge path 11 is connected to the first outlet 10 a 1. The other end of the first discharge path 11 is connected to a condenser 12. The first discharge path 11 discharges the steam from the expander 10, and introduces the discharged steam into the condenser 12. The condenser 12 condenses the steam by cooling the steam, and produces the liquid refrigerant. The condenser 12 receives blast by a fan 13 and can cool and condense the steam efficiently. Arranged under the condenser 12 is a condensed water tank 14 that reserves the liquid refrigerant produced in the condenser 12.

One end of a second discharge path 15 is connected to the second outlet 10 a 2. The other end of the second discharge path 15 is connected to the condensed water tank 14. The above-described second discharge path 15 discharges the liquid refrigerant from the expander 10 to the condensed water tank 14. The liquid refrigerant that has been cooled in the condenser 12 is reserved in the condensed water tank 14. The liquid refrigerant condensed in the expander 10 is mixed with the liquid refrigerant cooled in the condenser 12 and its temperature is decreased by being discharged to the condensed water tank 14. A flow passage area S2 of the second discharge path 15 is smaller than a flow passage area S1 of the first discharge path 11. That is to say, a relation of S2<S1 is established.

At a downstream side of the condensed water tank 14, provided is a refrigerant recovery passage 16 that re-circulates the liquid refrigerant, which is temporarily reserved in the condensed water tank 14, to the engine 1 side. The refrigerant recovery passage 16 is connected to the upstream side of the first water pump 6 in the refrigerant circulating path 5. A second water pump 17 is arranged in the refrigerant recovery passage 16. The second water pump 17 is an electric vane pump. When the second water pump 17 is in an operational state, the liquid refrigerant in the condensed water tank 14 is supplied to the refrigerant circulating path 5. In addition, a unidirectional valve 18 that prevents reverse flow of the refrigerant is provided downstream of the second water pump 17. As described above, the Rankine cycle system 100 includes a passage where the refrigerant is circulated.

The relation of D2<D1 is established between the diameter D1 of the first outlet 10 a 1 included in the Rankine cycle system 100 and the diameter D2 of the second outlet 10 a 2 as described previously. In addition, the relation of S2<S1 is established between the flow passage area S1 of the first discharge path 11 included in the Rankine cycle system 100 and the flow passage area S2 of the second discharge path 15. Maintaining the above relations is effective for preventing the steam from passing through the second outlet 10 a 2. In the Rankine cycle system 100, it is desirable that the steam supplied into the expander 10 is discharged from the first outlet 10 a 1 as much as possible. If the steam, which is vaporized refrigerant not condensed, is discharged from the second outlet 10 a 2, the steam passes through the second discharge path 15 and the condensed water tank 14, and flows into the condenser 12. That is to say, the steam flows from a direction different from a designed inflow direction into the condenser 12. If the steam flows into the condenser 12 from the direction different from the designed direction as described above, the function of the condenser 12 is impaired. That is to say, the condenser 12 cools and condenses the steam by heat exchange before the steam which has been introduced from the upper side thereof reaches the condensed water tank 14, and produces the liquid refrigerant. If high-temperature steam flows from the condensed water tank 14 side, the function of the condenser 12 is impaired. Moreover, the temperature of the liquid refrigerant in the condensed water tank 14 rises. The liquid refrigerant in the condensed water tank 14 is supplied to the engine 1 again, and used for cooling the engine 1. Thus, it is required to keep the temperature of the liquid refrigerant in the condensed water tank 14 as low as possible.

The Rankine cycle system 100 satisfies a relation expressed by a following equation (1) in order to prevent the steam from being discharged from the second outlet 10 a 2.

Δh>ΔPto/ρg  equation (1)

Δh: difference between a liquid level in the condensed water tank 14 and a lowest liquid level in the second discharge path 15 ΔPto: pressure loss when the steam flows in the condenser 12 from the expander 10 through the first discharge path 11 ρ: density of the liquid refrigerant g: gravitational acceleration

Here, Δh in the present embodiment is equal to Δh1 as illustrated in FIG. 1 and FIG. 2. In addition ΔPto in the present embodiment is a pressure loss within a range indicated by B in FIG. 1 and FIG. 2.

It is possible to prevent the steam from being discharged from the second outlet 10 a 2 by satisfying the relation expressed by the equation (1). To satisfy the relation of the equation (1), it is effective to make the value of Δh as large as possible, and the value of ΔPto as small as possible. It is possible to make the value of ΔPto small by setting the diameter D1 of the first outlet 10 a 1 large or setting the flow passage area S1 of the first discharge path 11 large.

On the other hand, the second discharge path 15 may be replaced with a second discharge path 151 illustrated in FIG. 3 in order to set Δh large. As illustrated in FIG. 3, a connected position P1 of the second discharge path 151 to the condensed water tank 14 is located higher than a lowest liquid level 151 a in the second discharge path 151. The lowest liquid level 151 a is lowered by making the second discharge path 151 have a U-shape. This secures Δh2. As apparent from FIG. 3, Δh2 is larger than Δh1 when the second discharge path 15 is used. As a result, Δh2 easily satisfies the condition of the equation (1).

As described above, according to the Rankine cycle system disclosed in the present specification, it is possible to discharge the liquid refrigerant produced in the expander 10 efficiently. As a result, it is possible to suppress deterioration and damage of the expander caused by production of the liquid refrigerant in the expander 10. At this time, a special control device for discharging the liquid refrigerant from the expander 10 is not necessary, and there is an advantage in cost.

The above described embodiments are merely examples for carrying out the present invention, and the present invention is not limited to the above-mentioned embodiments, and it is apparent from the above descriptions that other embodiments, variations and modifications may be made without departing from the scope of the present invention.

DESCRIPTION OF LETTERS OR NUMERALS

-   -   1 . . . engine     -   2 . . . exhaust pipe     -   3 . . . steam pathway     -   3 a 1 . . . steam discharge pipe     -   4 . . . gas-liquid separator     -   5 . . . refrigerant circulating path     -   6 . . . first water pump (W/P)     -   7 . . . liquid refrigerant pathway     -   8 . . . superheater     -   8 a . . . vaporizing portion     -   8 b . . . superheating portion     -   9 . . . nozzle     -   10 . . . expander     -   10 a . . . turbine chassis     -   10 b . . . turbine blade     -   11 . . . first discharge path     -   12 . . . condenser     -   13 . . . fan     -   14 . . . condensed water tank     -   15, 151 . . . second discharge path     -   16 . . . refrigerant recovery passage     -   17 . . . second water pump (W/P)     -   18 . . . unidirectional valve     -   100 . . . Rankine cycle system 

1. A Rankine cycle system comprising: a superheater, an expander that is driven by steam, which is vaporized refrigerant supplied from the superheater, to recover energy, and includes a first outlet discharging steam and a second outlet discharging liquid refrigerant produced by condensation of the steam in the expander; a first discharge path that is connected to the first outlet and discharges the steam from the expander; a condenser into which the steam is introduced through the first discharge path, and that condenses the steam into liquid refrigerant, a condensed water tank that reserves the liquid refrigerant produced in the condenser; and a second discharge path that connects the second outlet to the condensed water tank and discharges the liquid refrigerant from the expander, wherein a liquid level in the condensed water tank satisfies a following relation: Δh>ΔPto/ρg, when a height difference between the liquid level and a lowest liquid level in the second discharge path is expressed by Δh, a pressure loss when the steam flows into the condenser from the expander through the first discharge path is expressed by ΔPto, a density of the liquid refrigerant is expressed by ρ, and a gravitational acceleration is expressed by g.
 2. The Rankine cycle system according to claim 1, wherein the second outlet is provided to a downside portion of the expander.
 3. (canceled)
 4. The Rankine cycle system according to claim 1, wherein a connected position of the second discharge path to the condensed water tank is located higher than the lowest liquid level in the second discharge path.
 5. The Rankine cycle system according to claim 1, wherein a diameter of the second outlet is smaller than a diameter of the first outlet.
 6. The Rankine cycle system according to claim 1, wherein a flow passage area of the second discharge path is smaller than a flow passage area of the first discharge path. 